@philiprehberger/ts-match

Pattern matching for TypeScript -- switch on steroids

Installation

npm install @philiprehberger/ts-match

Usage

import { match, P } from "@philiprehberger/ts-match";

// Literal matching
const label = match(statusCode)
  .with(200, () => "OK")
  .with(404, () => "Not Found")
  .with(500, () => "Server Error")
  .otherwise(() => "Unknown");

// Type matchers
const type = match(value)
  .with(P.string, () => "string")
  .with(P.number, () => "number")
  .with(P.boolean, () => "boolean")
  .otherwise(() => "other");

// Object shape matching
const message = match(event)
  .with({ type: "login", user: P.select("name") }, (_v, sel) => `Welcome ${sel.name}`)
  .with({ type: "logout" }, () => "Goodbye")
  .exhaustive();

// Guard predicates
const size = match(count)
  .with(P.when((n) => n > 100), () => "large")
  .with(P.when((n) => n > 10), () => "medium")
  .otherwise(() => "small");

// Union matching
const color = match(input)
  .with(P.union("red", "green", "blue"), () => "primary")
  .otherwise(() => "other");

// Array matching
const result = match(data)
  .with(P.array(P.number), (nums) => nums.reduce((a, b) => a + b, 0))
  .otherwise(() => 0);

// Regex matching on strings
const kind = match(token)
  .with(P.regex(/^user-\d+$/), () => "user")
  .with(P.regex(/^admin-\d+$/), () => "admin")
  .otherwise(() => "other");

// Exhaustive matching (throws if no pattern matches)
const output = match(action)
  .with("start", () => startProcess())
  .with("stop", () => stopProcess())
  .exhaustive();

API

Export	Description
match(value)	Start a match expression, returns a chainable builder
.with(pattern, handler)	Add a match case; handler receives (value, selections)
.otherwise(handler)	Default case; always matches, returns handler result
.exhaustive()	Finalize; throws if no pattern matched
.run()	Alias for .exhaustive()
P.string	Matches any string
P.number	Matches any number
P.boolean	Matches any boolean
P.nullish	Matches null or undefined
P.any	Matches any value
P.when(fn)	Matches when fn(value) returns true
P.union(...values)	Matches if any value/pattern in the union matches
P.instanceOf(Class)	Matches instances of the given class
P.select(name?)	Captures the matched value into selections
P.array(pattern)	Matches arrays where every element matches the pattern
P.regex(re)	Matches strings against the given regular expression

Development

npm install
npm run build
npm test

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License

MIT